Driving an SCR directly from a 555 a good idea?

Discussion in 'Digital Circuit Design' started by Ritalie, Sep 5, 2016.

  1. Ritalie

    Thread Starter New Member

    Sep 5, 2016
    I'm making a magnetic pulse coil, and it will be discharging 350 volts into a 2.5 mH coil made from 16 gauge wire, from a 270uF capacitor. I have searched but cannot find any information about SCR feedback. Can the SCR ruin a 555 timer? Should I use a transistor or mosfet to drive the SCR?

    The SCR is rated for 800 volts, 800 amps surge. Just to be safe, I'm planning on using an IRF840 mosfet to drive the SCR.
  2. Dodgydave

    AAC Fanatic!

    Jun 22, 2012
    Best thing is to show us your circuit diagram, then we can assist you further.
  3. ian field

    Distinguished Member

    Oct 27, 2012
    Might be possible to get a triac or SCR output optocoupler capable of driving the gate on your SCR.

    Then all you're driving with the 555 is the IRLED in the optocoupler - and it gives you complete isolation.

    BTW: if it a rail gun - that contravenes the forum terms & conditions.
  4. Ritalie

    Thread Starter New Member

    Sep 5, 2016
    Hello, I'm not making a magnetic rail gun. I am making a coil of wire that is driven by a capacitor discharge, pulsed from an SCR at regular intervals. This is a Bob Beck circuit. So my question was, is it normal to drive an SCR using a 555 timer? The Optocoupler sounds like a neat idea. I'll look into that!
  5. Bernard

    AAC Fanatic!

    Aug 7, 2008
    Subject to review, if SCR cathode is at same ground as 555 I see no reason not to use direct drive. I would use a 27 ohm R between pin 3 & gate. Cap. neg. will be at ground for easy charging.
    If isolation is necessary, use 1:1 pulse transformer.